CGKEYCHIP Custom Keypad

CGKEYCHIP1

The Maximite design uses a PS/2 connection as a keyboard interface. You can use a full keyboard connected to either a CGCOLORMAX or the CGMMSTICK.

If you want to embed either of these two setups into a project, you might choose to replace the full keyboard with something either more compact or custom for your application. The CGKEYCHIP1 wired into a “ColorMax” or “stick” lets you create your own keyboard by adding your own buttons.

The CGKEYCHIP1 is a 24 pin chip in a DIP (through-hole) package. Four wires connect to the Maximite that include ground, power, and the two PS/2 communication signals (data/clock). You can wire in twelve distinct buttons for the keyboard keys plus three “modifier” buttons.

The CGKEYCHIP1 has two sets of keys that it can transmit:

Set1
F1
F2
F3
F4
F5
F6
F7
F8
F9
F10
F11
F12

Set2
Up Arrow
Down Arrow
Left Arrow
Right Arrow
Space Bar
Page Up
Page Down
Enter
End
Home
Tab
Backspace

An input pin on the chip selects between these sets of keys.

The CGKEYCHIP1 runs off of the 5V that the PS/2 connection provides. Both chip grounds should be connected to ground. The pins marked “NoConnect” should not be connected to anything.

Supplied with the CGKEYCHIP1 is a 1.3 kohm resistor that has to be connected from pin 11 to pin 15 for the chip to operate correctly

The PS/2 data signals are open-collector signals. When you connect the GCKEYCHIP to a CGCOLORMAX there are pull up resistors already on the ColorMax. When you connect to a CGMMSTICK and CGVGAKBD1 combination, the CGVGAKBD1 board already has pull up resistors in place for the two PS/2 lines. No additional resistors are needed in this case.

CGKEYCHIP1 pinout.

When you connect the CGKEYCHIP1 to just a CGMMSTICK, you will need to attach two pull-up resistors in order to have the chip function correctly. Each of the two PS/2 lines should be pulled to 5V through a 10 kohm resistor.

Example CGKEYCHIP1 schematic.

The SetSelect input to the CGKEYCHIP1 selects the key set that you wish to use, either set 1 or set 2. Connecting this input directly to 5V will select set 1, while connecting this input to ground selects set 2.

The key inputs are activated by momentary contact to ground. Simple SPST buttons can be used.

You can write a very simple MMBasic program to check the codes that the keys transmit against the list of codes found in this document:

When run, set 1 will return these codes:

Set 2 returns these codes :

MMBasic interprets the Alt as a key by itself, not a modifier. The keycode for the Alt key is 139, Control-Alt is 203, Shift-Alt is 171, Control-Shift-Alt is 235. This program will return two key codes when Alt is used, first the Alt code, then the key code. Control-Shift-Alt-F1, for example, returns 235 241.

Example of circuit board ready for CGKEYCHIP1